Device and method for assembling a structure at sea

ABSTRACT

A device for assembling a large structure at sea, particularly a wind turbine. The device includes a support structure which can be arranged relative to a transport vessel, wherein a part of the support structure is movable from a transport position, in which the component is transported, to an assembly position in which the component is rotated and/or tilted relative to the transport position. The movable part is provided can be fixed in place. A method for assembling a large structure at sea making use of the device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Belgian Patent Application No. 2009/0330,filed May 28, 2009, which is hereby incorporated by reference in itsentirety. Priority is not being claimed.

FIELD OF THE INVENTION

The invention relates to a device for assembling a structure at sea. Theinvention also relates to a method for assembling a structure at sea.The invention relates particularly to a device and method for assemblinga wind turbine at sea.

BACKGROUND OF THE INVENTION

A growing number of structures must be constructed, maintained andrepaired at sea. A typical example is an offshore wind turbine which isconstructed from a gondola or nacelle which is supported by a mast whichcan be over 100 metres high. The mast comprises different mast segmentsgenerally placed successively one onto another. The gondola is thehousing on the mast in which a large part of the necessary equipment islocated and which alone can already have a weight of more than 350 tons.The wind turbine is further provided with a hub on which a number ofrotor blades are arranged. The hub forms the connection between therotor blades of the wind turbine and the shaft thereof. The rotorblades, which can have a length of more than 70 metres, convert thekinetic energy of the wind into a rotating movement of the shaft. Thecurrently very common wind turbines are equipped with three rotorblades, wherein the rotor blades can rotate over their longitudinalaxis. They can hereby take up the optimal position at any wind speed,thereby achieving an optimum production. They can in this way also berotated out of the wind at high wind speeds by means of a so-calledpitch installation. A typical wind turbine is further provided with atransmission or gearbox to adjust the generator rotation speed (50 Hz)to the rotation speed of the rotors. The generator converts the movementof the shaft into electricity and supplies the generated power to thepublic grid.

During the assembly, maintenance and/or repair of such large structuresat sea it is usual to transport components of the structure to anoffshore jack-up platform moored in the vicinity of the location wherethe structure is situated or must be constructed. For the constructionof for instance a wind turbine the mast components and an assembly ofrotor blades arranged on a hub are navigated to the location ofconstruction using a suitable vessel. The jack-up platform is providedwith a lifting device which can lift the supplied components from thetransport vessel and can carry them to the structure to be constructed.

During the lifting and placing of components it is usual for these tohave to be placed at least temporarily in a position other than thetransport position. Components must more particularly be manipulated inorder to move them from their transport position (the position in whichthe relevant component was transported) to their assembly position (theposition in which the relevant component is added onto or to an alreadyexisting construction). During lifting and placing of wind turbine rotorblades onto an already existing or constructed mast the jack-up platformis thus provided with an auxiliary crane (a so-called tailing crane)which ensures that the assembly of hub and (for instance three) rotorblades is erected at least partially in vertical direction from thehorizontal transport position in order to enable arranging of thisassembly on the mast. An outer end of a rotor blade is here secured tothe tailing crane.

The known device and method are time-consuming. The tailing cranemoreover takes up a great deal of space on the platform, wherebyvaluable space is lost. In addition, working with a tailing cranerequires good coordination and skill, a lack of which may result indanger.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a device with which(components of) large structures, and particularly wind turbines, can beassembled at sea.

This object is achieved by providing a device for assembling a largestructure at sea, particularly a wind turbine, which device comprises asupport structure for a component of the structure which can be arrangedon a transport vessel, wherein a part of the support structure ismovable from a transport position, in which the component istransported, to an assembly position in which the component is rotatedand/or tilted relative to the transport position, wherein the movablepart is also provided with fixing means for fixing of the component.

The invention likewise relates to a method for assembling a largestructure at sea, particularly a wind turbine, making use of the deviceaccording to the invention. The method comprises of providing a deviceaccording to the invention on a transport vessel, arranging a componentof the structure on the movable part of the device using the fixingmeans, transporting the component to the location at sea where thecomponent must be assembled using the transport vessel, wherein thecomponent is situated in a transport position during the transport,optionally rotating and/or tilting the movable part of the supportstructure from the transport position to an assembly position, whereinthe component is rotated and/or tilted relative to the transportposition, and arranging the component on the structure in the assemblyposition. Moving the movable part of the support structure from thetransport position to an assembly position preferably takes place aftermooring of the vessel in the immediate vicinity of the structure to beassembled, and particularly against a jack-up offshore platform mooredin the vicinity of the construction location, the platform beingprovided if desired with a lifting device which can pick up the suppliedcomponents from the transport vessel and carry them to the structure tobe constructed. It is however also possible for the transport vessel toalso serve as mooring platform.

In a further embodiment of the method the transport position cancorrespond to the assembly position. The component is thus transportedin the assembly position, whereby rotation or tilting from the transportposition to the assembly position is not necessary.

The component to be transported, rotated and/or tilted can in principlebe any component of the structure. The method is particularly suitablefor wind turbines wherein the components to be transported, rotatedand/or tilted can for instance comprise a gondola or nacelle, and/or ahub, and/or one or more rotor blades.

The use of a tailing crane is avoided by providing a support structurewith a movable part, on which part the component can be arranged. Afurther advantage is that the component can also be placed in anydesired angular position relative to the deck of the transport vesselduring transport. This improves convenience and safety during transport.

The movable part can in principle be rotatable and/or tiltable aroundany axis. It is thus possible to provide a movable part which isrotatable and/or tiltable around a vertical axis. This allows placing ofthe component in an optimal position for the transport and/or for themounting during the assembly of the structure.

A preferred embodiment of the device according to the invention ischaracterized in that the movable part is tiltable around a horizontalaxis. This is particularly useful for the assembly of a wind turbine atsea, wherein an assembly of wind turbine rotor blades must be moved froma transport position, in which the rotor blades extend substantiallyparallel to the deck of the transport vessel, to an assembly position inwhich the rotor blades extend substantially perpendicularly of the deckof the transport vessel.

A further preferred embodiment of the device according to the inventionis characterized in that the movable part is rotatable around ahorizontal axis. This is particularly useful for the assembly of a windturbine at sea, wherein an assembly of wind turbine rotor blades must bemoved from a transport position, in which the rotor blades extendsubstantially perpendicularly of the deck of the transport vessel, to anassembly position in which the rotor blades still extend substantiallyperpendicularly of the deck of the transport vessel but are rotatedrelative to the transport position.

In another preferred embodiment the support structure of the deviceaccording to the invention comprises a tower, wherein the rotatable partis situated at the top of the tower. Such an embodiment allows the hubof an assembly of rotor blades to be placed at a height such that, whenrotor blades are placed in the assembly position, they do not come intocontact with the deck of the transport vessel or with other componentssuch as the jack-up platform. The tower can in principle be embodied inany manner. The tower can thus be static or movable. It is advantageousto embody the tower as a static structure, for instance in the form of aframework, or as a beam structure which if desired comprises differentrotatable beam segments pivotable relative to each other. Such anembodiment is stable, strong and relatively inexpensive. A framework ismoreover light and can be erected as desired in simple manner.

A preferred embodiment of the device according to the inventioncomprises a tower which is height-adjustable. Not only can components ofdifferent dimensions hereby be transported and rotated, the height canmoreover be adjusted subject to the conditions on site, such as forinstance the desired transport and/or assembly position.

The jack-up offshore platform and/or the transport vessel generallycomprise a work deck which can bear a substantial load and anchor pileswhich support the work deck. Each anchor pile extends substantiallyvertically and is movable in this direction from a high position duringtransport to a low position in the anchored position, in which positionthe piles support on the seabed. The height position of the work deckrelative to the water level can be changed by shifting the work deckrelative to the piles by means of hydraulic pistons. In the anchoredposition the work deck can be jacked up to a position above the waterlevel. It is however also possible to only stabilize the platform. Sucha platform is only partially jacked up to a level at which the pilessupport on the seabed but the work deck still partially makes contactwith the water. A platform stabilized in this manner can take a lighterform because part of the load is supported by the water.

A component of almost any dimension can in principle be manipulated withthe device according to the invention. A preferred embodiment relates toa tower with a maximum height of at least 20 metres above the work deckof the transport vessel, more preferably at least 30 metres, still morepreferably at least 40 metres.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be elucidated in more detail with reference tothe accompanying figures, without otherwise being limited thereto. Inthe figures:

FIG. 1A is a schematic side view of an embodiment of the deviceaccording to the invention during transport;

FIG. 1B is a schematic side view of a second embodiment of the deviceaccording to the invention during transport;

FIG. 2A is a schematic side view of the embodiment shown in FIG. 1Aduring assembly; and

FIG. 2B is a schematic side view of the embodiment shown in FIG. 1Bduring assembly; and

FIG. 3 is a schematic top view of the embodiment of the device accordingto the invention shown in FIG. 2A during assembly.

DETAILED DESCRIPTION

Referring to FIG. 1A, a device is shown for assembling a wind turbine 50at sea. The device comprises a support structure 20 arranged on atransport vessel in the form of a jack-up platform 10, wherein a part 24of support structure 20 is tiltable around a horizontal axis in theindicated direction R1 by means of a hinge connection 25. Rotatable part25 is provided with fixing means (not shown), such as for instancebolts, for the fixing a component of wind turbine 50, and in particularrotor 55. Rotor 55 comprises an assembly of a hub 56, on which threerotor blades (56 a, 56 b, 56 c) are mounted. It is also possible for hub56 to be provided with only one, two or, conversely, more than threerotor blades. Rotatable part 24 can be moved from a transport positionas shown in FIG. 1A, in which rotor 55 with the rotor blades istransported in horizontal position, to an assembly position as shown inFIG. 2A by being tilted around hinge 25. The necessary force can forinstance be provided by hydraulic piston 26, although any other suitablemethod of force transmission is also possible. In the shown embodimentthe transport position corresponds to a position in which the rotorblades (57 a, 57 b, 57 c) extend substantially parallel to deck 27 ofplatform 10, while the assembly position corresponds to a position inwhich the rotor blades (57 a, 57 b, 57 c) extend substantiallyperpendicularly of deck 27 of platform 10.

Referring to FIG. 1B, the device as already shown in FIG. 1A is shown.In this embodiment however, part 24 of support structure 20 is placed inthe upright tilted position, whereby the transport position correspondsto a position in which the rotor blades (57 a, 57 b, 57 c) extendsubstantially perpendicularly of deck 27 of platform 10. Rotor 55 istherefore transported into vertical position. According to the presentembodiment, part 24 is likewise rotatable around a horizontal axis sothat rotor 55 can be anchored in different rotation positions (in thedirection R2). The transport position shown in FIG. 2B corresponds to aposition rotated in the direction R2, in which one rotor blade 57 c isplaced substantially vertically and the two remaining rotor blades (57a, 57 b) are placed at the same angle to the water surface. In thisposition the distance from hub 56 of rotor 55 to the top of the tworotor blades (57 a, 57 b) is minimal, whereby hub 56 need not be placedvery high above the water surface.

Rotor 55 can be moved from the vertical transport position shown in FIG.1B, in which one rotor blade 57 c is placed substantially vertically, tothe assembly position shown in FIG. 2B by rotating the part 24 in thedirection R2. In the shown embodiment the transport position correspondsto a position in which rotor blade 57 a extends substantially verticallyand protrudes over the edge of platform 10. Rotor blades (57 b, 57 c)extend at substantially the same angle to the water surface. Thisassembly position is advantageous for the manipulation of rotor 55 witha lifting device 30.

The support structure of the device according to the invention comprisesa tower in the form of a framework 20 provided with uprights 22 andtransverse beams 23, the cross-sections of which are large enough to beable to support the necessary loads. In the shown embodiment movablepart 24 is situated on top of tower framework 20. This latter ispreferably height-adjustable, wherein the height 21 of tower 20 withrotor 55 will generally be lower in the transport position (FIG. 1) thanthe height 21 of tower 20 with rotor 55 in the assembly position (FIG.2). The maximum height of tower 20 can be freely chosen. In view of thedimensions of rotor blades, the maximum height of tower 20 is preferablyat least 20 metres above work deck 27 of transport vessel 10, morepreferably at least 30 metres, and most preferably at least 35 metresabove work deck 27 of transport vessel 10.

The jack-up offshore platform 10 comprises a work deck 27 which can beara substantial load, typically of more than 1000 tons, and is providedwith anchor piles 3 which support work deck 27. Each anchor pile 3extends substantially vertically and is movable in this direction from ahigh position during transport (shown in FIG. 1) to a low position inthe anchored position (shown in FIG. 2), in which position piles 3support on seabed 200. The height position of work deck 27 relative towater level 100 can be changed by shifting work deck 27 relative topiles 3 by means of hydraulic pistons 4.

Transport vessel or platform 10 provided with the device according tothe invention is generally moored in the immediate vicinity of a secondjack-up platform 101 as shown in FIG. 2. Parts of platform 101comparable to parts of platform 10 are designated in the figures withthe same numerals as those of platform 10 and not further describedhere. Reference is made to the description thereof in respect ofplatform 10.

Platform 101 is anchored in the immediate vicinity of the wind turbine50 to be assembled and/or maintained, which is shown in semi-finishedstate and which is anchored in seabed 200 by foundation 51. In the shownsemi-finished state wind turbine 50 comprises, in addition to foundation51, two mast parts (52, 53) and a gondola 54. Mast parts (52, 53) andgondola 54 have already been put in place by a lifting device 30provided on platform 101. Any suitable lifting device 30 can inprinciple be applied. In the shown embodiment lifting device 30substantially comprises two parts. The first part comprises a structurewhich is connected pivotally to point of rotation 13 a and whichcomprises at least a main boom 14 for manipulating rotor 55 of windturbine 50. A turntable 11 is provided which can rotate main boom 14around a vertical axis 12 relative to platform 101. Lifting device 30further comprises a frame 13 which supports main boom 14 in rotatablemanner and a second boom 15. Additional booms 16 can likewise rotatearound point of rotation 14 a of main boom 14. The booms are mutuallyconnected by means of cables. Rotor 55 can be secured to the liftingdevice by means of gripper means 17 and then be manipulated, forinstance lifted, rotated and so on. Lifting device 101 also comprises acounterweight 32 which is connected to frame 13 for movement from aposition toward and away from point of rotation 13 a of main boom 14.Optionally incorporated in the cables are force sensors (not shown)which are connected to a control system for regulating the cabletension.

According to the embodiment of the invention shown in the figures, amethod is provided for assembly of a wind turbine 50 at sea. The methodcomprises of providing a transport vessel 10 as shown in FIG. 1A,arranging rotor 50 of wind turbine 50 on movable part 24 of the deviceusing the fixing means (not shown), transporting rotor 50 usingtransport vessel 10, wherein rotor 50 is situated in a preferablyhorizontal transport position (substantially parallel to work deck 27),tilting movable part 24 around a horizontal axis R from the transportposition shown in FIG. 1A to the assembly position shown in FIG. 2A,wherein rotor 50 is rotated relative to the transport position andpreferably extends substantially perpendicularly of work deck 27 ofplatform 10. An alternative method comprises of providing a transportvessel 10 as shown in FIG. 1B, arranging rotor 50 of wind turbine 50 onmovable part 24 of the device using the fixing means (not shown),transporting rotor 50 using transport vessel 10, wherein rotor 50 issituated in a vertical transport position (substantially perpendicularlyof work deck 27), rotating movable part 24 around a horizontal axis R2from the transport position shown in FIG. 1B to the assembly positionshown in FIG. 2B, wherein rotor 50 is rotated relative to the transportposition.

By moving rotor 50 from the transport position shown in FIGS. 1A and 1Bto the assembly position (this position is shown in FIGS. 2A and 2B) itcan be transferred easily to the semi-finished wind turbine 50 by meansof lifting device 30 and arranged thereon in the assembly position (theassembly position during arranging is shown schematically in FIGS. 2Aand 2B by the rotor in broken lines). During transfer of rotor 50 thelifting device will be moved from a position 30-1 to a position 30-2(FIG. 3). In position 30-1 rotor 55 is already in the assembly position.The method and device according to the invention avoid the use oftailing cranes present on platform 10 and/or 101 in the existing method.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments and those skilledin the art will be able to design many alternative embodiments withoutdeparting from the scope of the appended claims. In the claims, anyreference signs placed between parentheses shall not be construed aslimiting the claim. Use of the verb “to comprise” and its conjugationsdoes not exclude the presence of elements or steps other than thosestated in a claim. The article “a” or “an” preceding an element does notexclude the presence of a plurality of such elements. The invention maybe implemented by means of hardware comprising several distinctelements, and by means of a suitably programmed computer. In the deviceclaim enumerating several means, several of these means may be embodiedby one and the same item of hardware. The mere fact that certainmeasures are recited in mutually different dependent claims does notindicate that a combination of these measures cannot be used toadvantage in the figures, and many variants thereof are possible withinthe scope of protection of the appended claims.

1. Device for assembling a large structure at sea, particularly a windturbine, which device comprises a support structure for a component ofthe structure which can be arranged on a transport vessel, wherein apart of the support structure is movable from a transport position, inwhich the component is transported, to an assembly position in which thecomponent is rotated and/or tilted relative to the transport position,wherein the movable part is also provided with fixing means for fixingof the component.
 2. Device as claimed in claim 1, wherein the movablepart is tiltable around a horizontal axis.
 3. Device as claimed in claim2, wherein the movable part is rotatable around a horizontal axis. 4.Device as claimed in claim 1, wherein the support structure comprises atower and the movable part is situated at the top of the tower. 5.Device as claimed in claim 4, wherein the tower is height-adjustable. 6.Device as claimed in claim 4, wherein the tower has a maximum height ofat least 30 metres above the work deck of the transport vessel. 7.Device as claimed in claim 5, wherein the tower has a maximum height ofat least 30 metres above the work deck of the transport vessel. 8.Method for assembling a large structure at sea, particularly a windturbine, the method comprising of providing a device as claimed in anyof the foregoing claims on a transport vessel, arranging a component ofthe structure on the movable part of the device using the fixing means,transporting the component using the transport vessel, wherein thecomponent is situated in a transport position, optionally moving themovable part of the support structure from the transport position to anassembly position, wherein the component is rotated and/or tiltedrelative to the transport position, and arranging the component on thestructure in the assembly position.
 9. Method as claimed in claim 8,wherein the movable part of the support structure is moved from thetransport position to the assembly position such that the component istilted around a horizontal axis relative to the transport position. 10.Method as claimed in claim 8, wherein the movable part of the supportstructure is moved from the transport position to the assembly positionsuch that the component is rotated around a horizontal axis relative tothe transport position.
 11. Method as claimed in claim 8, wherein thecomponent to be transported, rotated and/or tilted comprises a gondolaor nacelle, and/or a hub, and/or one or more rotor blades of a windturbine.
 12. Method as claimed in claim 10, wherein the component to betransported, rotated and/or tilted comprises a gondola or nacelle,and/or a hub, and/or one or more rotor blades of a wind turbine.